Declining mortality over the past several decades has contributed to an increase in the proportion of persons over 64 in the US population, especially of persons over 84, the "oldest old." This aging trend is expected to continue for the foreseeable future. Since aging is associated with an increased incidence and prevalence of chronic disease, many health scientists predict that the demand for medical care will steadily increase in the years ahead. Others, however, believe that improvements in health care and reductions in risk factors are delaying the onset of chronic disease more than they are delaying death; thus, the interval between onset of disease and death is being compressed, resulting in a decreased demand for medical care services. The proposed research will compare the nine-year mortality, incidence and prevalence of chronic disease, and health services of a 1971 cohort that of a 1980 cohort. Each cohort will consist of 3000 randomly selected members of the Northern California Kaiser Permanente Medical Care Program aged 65 and over who have had at least one prior Multiphasic Health Checkup. Approximately one-third of each cohort will be 80 or older. Information on chronic disease diagnosis, cause-specific mortality, physiological and socio-demographic risk factors, and health services utilization will be obtained from computerized hospitalization and Multiphasic Health Checkup records and from medical charts. We will examine the hypotheses that in the 1980 cohort mortality is lower, chronic disease morbidity is lower, reductions in morbidity exceed reductions in mortality, and use of health services is lower. The study will be done by a team of experienced investigators on a sample of members of the largest HMO in the United States, with a high level of organizational commitment.